A fuel cell using a polymer electrolyte generates power and heat at the same time by electrochemically reacting a fuel gas containing hydrogen with an oxidizer gas containing oxygen such as air. This fuel cell is basically constituted of a polymer electrolyte membrane which selectively transfers hydrogen ions and a pair of electrodes, that is an anode and a cathode, formed on both surfaces of the polymer electrolyte membrane. These electrodes are respectively provided with a catalyst layer which contains, as its major component, a carbon powder carrying a platinum group metal catalyst and is formed on the surface of a polymer electrolyte membrane and a gas diffusion layer which is arranged on the outside surface of the catalyst layer and has permeability and electron conductivity. A structure fabricated by assembling integrally a polymer electrolyte membrane with electrodes (including gas diffusion layers) in this manner is called an electrolyte membrane-electrode assembly (hereinafter referred to as “MEA”).
Separator plates which sandwich and fix the MEA mechanically and at the same time electrically connect neighboring MEAs in series with each other are arranged on both sides of the MEA. Gas flow passages which supply such a fuel gas and oxidizer gas to each of the electrodes and convey the produced water and excess gas out of the reaction system are formed on the separator plates at positions where the separators are in contact with the MEA. Though such gas flow passages may be formed separately from the separator plate, generally a groove is formed on the surface of the separator plate to form a gas flow passage. Here, such a structure in which the MEA is sandwiched between a pair of separators is called a single cell module.
The supply of reaction gas to the gas flow passage formed between the separator plate and the MEA as well as the discharge of reaction gas and produced water from the gas flow passage are conducted by forming a through-hole called a manifold hole and by communicating the outlet and inlet of the gas flow passage with the manifold hole to distribute the reaction gas from the manifold hole to each gas flow passage.
Further, a gas seal member or a gasket is arranged as a seal member between the pair of separators in such a manner as to surround the part where the electrodes are formed in the MEA, that is, the outer periphery of a power generation region in order to prevent the fuel gas and the oxidizer gas supplied to the gas flow passage from leaking out of the system and to prevent the two types of gases from being mixed. These gaskets seal the periphery of the manifold hole.
A fuel cell generates heat during operation and it is therefore necessary to cool it by cooling water or the like to maintain the battery in a good-temperature condition. Generally, a fuel cell is provided with one cooling section which flows cooling water every one to three cells. These MEAs, separator plates and cooling sections are alternately stacked, and after 10 to 200 cells are stacked, the stacked cells are sandwiched between end plates by interposing a current collecting plate and an insulating plate and fixed from both ends with fastening rods (bolts) in the structure of a usual stacked cell (fuel cell stack).
In such a stacked cell, a fastening manner is adopted such that a plurality of single cell modules including a cooling section are stacked in one direction, a pair of end plates are arranged on both sides of the stacked body and fastening rods (bolts) are used to fix these end plates, thereby fastening each single cell module. As such a fastening manner, a structure is adopted in which a metal material such as stainless steel is generally used for the end plates and fastening rods from the viewpoint of mechanical strength, and these end plates and fastening rods are electrically insulated from the stacked cell by insulating plates to prevent current from leaking out of the system by interposing the end plates. As to the fastening rods, they are passed through through-holes formed in the edge of the separator plates and the whole stacked cell is fastened with a metal belt by interposing the end plates.
In the stacked cell for which such a fastening manner is adopted, it is regarded as important to fasten the single cell module with in-plane (in a plane perpendicular to the stacking direction) uniform fastening force. The reason is that this uniform fastening force makes it possible to prevent leakage of, for example, air, hydrogen and cooling water and also the breakdown of the single cell module, thereby ensuring that generation efficiency can be enhanced and the life of the battery can be prolonged. From the viewpoint of making the fastening force uniform in this fastening manner, for example, Patent Document 1 proposes a method in which a spring is sandwiched between the X-shape fastening plates and a spring arranged in the center is made to have larger spring force than springs arranged in the periphery to thereby make the fastening force uniform. Also, in Patent Document 2, a method is proposed in which the parts which apply pressure are made to be in point contact with the end plate to thereby make the fastening force uniform. Further, besides the above, for example, various proposals are made as disclosed in Patent Documents 3 to 10.    Patent Document 1: JP-A No. 62-271364    Patent Document 2: JP-A No. 9-259916    Patent Document 3: JP-A No. 2007-113707    Patent Document 4: JP-A No. 61-248368    Patent Document 5: JP-A No. 09-270267    Patent Document 6: U.S. Pat. No. 4,997,728    Patent Document 7: U.S. Pat. No. 6,258,475    Patent Document 8: USP No. 2005/0277012    Patent Document 9: U.S. Pat. No. 4,973,531    Patent Document 10: USP No. 2007/0042250